手法を比較

	クロスオーバー自然実験	自然実験
分野	実験計画法	実験計画法
系統	Process / pipeline	Process / pipeline
提唱年	Crossover designs: mid-20th century; applied to natural experiments: 1990s–2000s	1990s (formal methodological articulation); earlier in epidemiology (John Snow, 1854)
提唱者	Drawn from crossover trial methods (Jones & Kenward) and natural experiment tradition (Mill, 1843; Dunning, 2012)	Varied; systematized in econometrics and political science (e.g., Meyer 1995; Angrist & Krueger 1991)
種類	Quasi-experimental design	Quasi-experimental research design
原典	Dunning, T. (2012). Natural Experiments in the Social Sciences: A Design-Based Approach. Cambridge University Press. ISBN: 978-1107698000	Meyer, B. D. (1995). Natural and quasi-experiments in economics. Journal of Business and Economic Statistics, 13(2), 151–161.
別名	within-unit natural experiment, reversal natural experiment, crossover quasi-experiment	natural quasi-experiment, naturally occurring experiment, exogenous shock design, as-if randomization
関連	5	3
概要	A crossover natural experiment exploits an externally imposed condition — a policy change, law, or environmental event — that exposes the same units (individuals, regions, firms) to both treatment and control states at different times. By observing each unit in multiple conditions, researchers use within-unit variation to estimate causal effects without researcher-controlled randomization, combining the internal validity advantage of crossover designs with the real-world relevance of natural experiments.	A natural experiment exploits a real-world event, policy, or circumstance that assigns individuals to treatment and control conditions in a way that is plausibly random — or at least exogenous to the outcome of interest. Because the researcher does not control assignment, it occupies a middle ground between a true randomized controlled trial and purely observational research, offering stronger causal leverage than conventional observational designs when the as-if randomization assumption holds.